Sandia National Laboratories chemical engineer Vicki Chavez worked with Kevin Fleming to prove that iron sulfate mixed with ammonium nitrate could produce a non-detonable fertilizer (Photo: by Randy Montoya)

Ammonium nitrate is a commonly used fertilizer, but when mixed with a fuel such as diesel, it makes a powerful explosive – as seen in last week’s fertilizer plant explosion in Texas. But it's the deliberate use of the compound in improvised explosive devices (IEDs) and acts of terror such as the Oklahoma City bombing that gives rise to even greater cause for concern. This is why Kevin Fleming, an optical engineer at Sandia National Laboratories, developed a fertilizer alternative that isn’t detonable and therefore can’t be used in a bomb.

The use of ammonium nitrate in IEDs is so widespread that the Joint Improvised Explosive Device Defeat Organization (JIEDDO) last year put out a call for ideas on ways to neutralize ammonium nitrate as an IED explosive. It’s a difficult task because its legal use is so common. Even though ammonium nitrate fertilizer is illegal in Afghanistan for example, it is easily sourced from neighboring Pakistan, where agriculture accounts for a quarter of the country’s gross domestic product.

Fleming, who retired from Sandia Labs in February, thought he had the right combination of knowledge and experience to tackle the problem. After years training soldiers in how to deal with IEDs, he knew the chemistry behind them. From the age of eight he also gained organic gardening experience dealing with calcareous soils similar to those found in the Middle East at his family’s five-acre property in Las Cruces, New Mexico.

Knowing that in ammonium nitrate the ammonium ion is weakly attracted to the nitrate ion, and that the right chemical reaction can pull them apart, Fleming decided to look for a compound they would rather cling to that could be added to the ammonium nitrate. He tried several materials, including iron sulfate, a readily available compound discarded by the ton from steel foundries.

If someone attempts to alter the ammonium nitrate/iron sulfate mixture to make it detonable by mixing it with fuel, the iron ion takes the nitrate ion and the ammonium ion takes the sulfate ion. The result is that the iron sulfate becomes iron nitrate and the ammonium nitrate becomes ammonium sulfate, neither of which is detonable.

But the new compound wouldn’t be much use if it weren’t also a good fertilizer. Thankfully, it is. In fact, the addition of iron sulfate to the mix makes the new fertilizer even better than ammonium nitrate for alkaline soils. These are what is found in Afghanistan, where a mix of ammonium nitrate and calcium carbonate is currently used, making the soil more alkaline.

“It takes alkaline soil and makes it more neutral, closer to an ideal pH level,” said Fleming of his non-detonable fertilizer. “The closer you get a neutral pH, the more crops grow. Crop yield would improve significantly. And iron-containing fertilizer added to the soil would be taken up in crops and help fight anemia and other iron deficiencies in people who eat them.”

Although Fleming says the non-detonable fertilizer would cost no more to produce than ammonium nitrate, he knows that it will take some time for the former to replace the latter in Afghanistan and other parts of the world given the sheer volume of ammonium nitrate production. However, he does have some ideas on how to get the ball rolling.

“We could give the formula to a neutral party and let them work with the Afghans, Pakistanis and others,” he said. “They could set up side-by-side demonstrations to see which fertilizer works better. Prove it to them gradually.”

Fleming has informed JIEDDO of the non-detonable fertilizer and, in the hopes of saving lives, Sandia isn’t licensing or patenting the formula but is making it freely available.

Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

Taking the article's claims at face value, this could be a pretty easy market-driven switch.

Fertilizer producers such as SCOTTS would be all over this if the claims of making acidic soil more productive at the same cost are verifiable.

It would be a no-brainer for them because it would be very marketable and that is the fastest path to rapid adoption.

Joseph Boe 26th April, 2013 @ 06:35 am PDT

Nice. The cool part about this is that countries that are now trying to keep Ammonium Nitrate out can switch to simply requiring that this additive be put in before import (turning a ban into a regulation).

How about using less fertilizer? The problems caused by fertilizer runoff from both large farming areas and urban lawns is a serious problem when it reaches streams and the ocean, causing blooms of algae that deplete oxygen and dead zones where no fish can survive. Implementing modern organic farming practices is a better solution than just making it easier and safer to use more fertilizer.

Jerry Peavy 26th April, 2013 @ 03:58 pm PDT

How difficult is it to separate ammonium nitrate from iron sulfate?

How difficult is it to extract toxins from the fertilizer fuel mix.

How toxic is the smoke.

Which is more dangerous.

Slowburn 26th April, 2013 @ 05:39 pm PDT

@ Joseph Boe

No, it makes ALKALINE soils more neutral. Iron sulphate is an acidifier.

And it won't blow up, so... the hapless terrorist would get a lungful of toxic gas.

Not a practical weapon there, either. Doesn't burn, would dilute in open air...

And the reaction wouldn't happen in normal use unless, of course, someone poured diesel fuel all over the field.

William Carr 27th April, 2013 @ 08:15 pm PDT

Sounds like a 'no brainer' to me ... I can't see any toxic side effects not being outweighed by the safety angle. Any and all fertiliser plants should have to use this recipe immediately, on pain of fines, sanctions or whatever can be imposed to encourage the idea. If it does not come from the factory, the terrorist should not be able to access the explosive version. Laws should be passed and funds made available to allow any present stocks stored in shops/warehouses etc to be 'recycled' at a subsidised cost so the consumer would not lose out. Remove the temptation to "just finish up that pallet" and half the problem goes away.

The Skud 28th April, 2013 @ 07:38 pm PDT

re; The Skud

Not all soil that ammonium nitrate will benefit will benefit from Ferric Nitrate.

Slowburn 28th April, 2013 @ 09:57 pm PDT

Preventing AN from being utilized as a weapon doesn't eliminate the cause of the violence, by any means. It just means the violent person takes another route. Banning guns, etc.. forces the perpetrator to get creative, and potentially discover even more dangerous and effective methods of injuring people in mass quantities. Infact, lets ban pressure cookers, or make them unable to achieve such high pressures, because that could be used as a weapon.

Charles Van Noland 29th April, 2013 @ 08:14 am PDT

I live in central North Carolina. The soils here, are naturally acidic, and of course suffer from acidic deposition. To grow a crop like maize, successfully, we already have to bring in crushed limestone from hundreds of miles away, and incorporate it into the soil of our fields. This "fertilizer" would increase the amount of lime required. The annual average number of people killed, or injured by ammonium nitrate fertilizer, bombs, is probably smaller than the number of people killed or injured, by bee stings every year. I've been using ammonium nitrate to grow food, since I was in elementary school. I have not blown up anything yet. This is one of the stupidest ideas I've ever heard of. Don't expect me to change the way I live, because of your absurd fear of terrorists. Use some critical thinking, will you.